CN113630166A - Method and apparatus for beam steering within a beamforming system - Google Patents

Abstract

Methods and apparatus are described. A method implemented in a wireless transmit/receive unit (WTRU), the method comprising: a first control information Search Space (SS) associated with a first set of standard beams including a first set of beams is monitored. After triggering based on measurements made by the WTRU, the WTRU initiates extended monitoring and monitors a control channel (SS) associated with an extended beam set including the first beam set and one or more additional beam sets. The WTRU determines a second set of beams from the extended set of beams. The determination is based on the received control channel beam switch command or on the control channel SS in which the beam switch command was received. The WTRU monitors a second control channel, SS, associated with a second standard set of beams including the determined second set of beams.

Description

Method and apparatus for beam steering within a beamforming system

The present application is a divisional application of chinese patent application No.201780014753.x entitled "method and apparatus for beam control in a beamforming system", filed on 3, month 2, 2017.

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional patent application No.62/302,962, filed 2016, 3, the contents of which are incorporated herein by reference.

Background

Frequencies above 6Ghz (such as mmW and cmW) are not used in cellular systems because of their propagation characteristics that have been considered detrimental to wireless communication in outdoor environments. In general, higher frequency transmissions will tend to experience higher free space path losses. Rainfall, atmospheric gases (e.g., oxygen), and vegetation may all further increase attenuation compared to frequencies below 6 GHz. In addition, transmission and diffraction attenuation may become more severe for frequencies above 6GHz than for frequencies below 6 GHz. This propagation characteristic for frequencies above 6GHz may result in significant non line of sight (NLOS) propagation path loss. For example, at mmW frequencies, the NLOS path LOSs may be more than 20dB higher than the line-of-sight (LOS) path LOSs, and may severely limit the coverage of mmW transmissions.

Recent channel measurements have shown the feasibility of outdoor mmW cell coverage with the help of beamforming techniques. The measurement data indicates that the beamforming gain may not only be able to provide the required coverage for cellular control signaling in NLOS conditions, but also to increase the link capacity to achieve higher data throughput in LOS conditions. Antennas implementing this beamforming technique may need to provide high gain, which may require a high degree of directivity, which may require the use of large electrically steerable antenna arrays at the transmitter and receiver.

Disclosure of Invention

Methods and apparatus are described. A method implemented in a wireless transmit/receive unit (WTRU), the method comprising: a first control information Search Space (SS) associated with a first standard (normal) set of beams comprising a first set of beams is monitored. After triggering based on the measurements of the WTRU, the WTRU initiates an extended monitoring and monitoring of a control channel (SS) associated with an extended beam set including the first beam set and one or more additional beam sets. The WTRU determines a second set of beams from the extended set of beams. The determination is based on the received control channel beam switch command or on the control channel SS within which the beam switch command was received. The WTRU monitors a second control channel, SS, associated with a second standard set of beams including the determined second set of beams.

Drawings

The invention will be understood in more detail from the following description, given by way of example, with reference to the accompanying drawings, in which:

FIG. 1A is a system diagram of an exemplary communication system in which one or more of the disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an exemplary wireless transmit/receive unit (WTRU) that may be used in the communication system shown in FIG. 1A;

fig. 1C is a system diagram of an example radio access network and an example core network that may be used in the communication system shown in fig. 1A;

FIG. 2 is a schematic diagram of an exemplary Orthogonal Frequency Division Multiplexing (OFDM) frame structure for an exemplary 1GHz system bandwidth;

fig. 3 is a schematic diagram of an exemplary single carrier frame structure for an exemplary 2GHz system bandwidth;

fig. 4 is a schematic diagram of an exemplary Phase Antenna Array (PAA) for full digital beamforming;

fig. 5 is a schematic diagram of an example of analog beamforming with one PAA containing one Radio Frequency (RF) chain for multiple antenna elements;

fig. 6 is a schematic diagram of an example of analog beamforming with one PAA and two RF chains;

fig. 7 is a schematic diagram of an example of analog beamforming with two PAAs and two RF chains;

fig. 8 is a schematic diagram of an example of analog beamforming with two PAAs and one RF chain;

FIG. 9 is a schematic diagram illustrating an example of elastic properties within an ultra-high density deployment;

FIG. 10 is a flow diagram of an exemplary method of wave velocity shaping and scheduling;

figure 11 is a flow diagram of an exemplary method for extended monitoring implemented in a WTRU;

FIG. 12 is a flow diagram of an exemplary method for extended monitoring implemented within a base station, such as a millimeter wave base station (mB); and

fig. 13A and 13B are diagrams 1300A and 1300B of more specific examples regarding extended monitoring.

Detailed Description

FIG. 1A is a schematic diagram of an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple-access system that provides content, such as voice, data, video, messaging, broadcast, etc., to a plurality of wireless users. Communication system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, communication system 100 may use one or more channel access methods, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), orthogonal FDMA (ofdma), single carrier FDMA (SC-FDMA), and so forth.

As shown in fig. 1A, the communication system 100 may include wireless transmit/receive units (WTRUs) 102a,102b,102c,102d, a Radio Access Network (RAN)104, a core network 106, a Public Switched Telephone Network (PSTN)108, the internet 110, and other networks 112, although it will be appreciated that any number of WTRUs, base stations, networks, and/or network elements are contemplated by the disclosed embodiments. Each of the WTRUs 102a,102b,102c,102d may be any type of device configured to operate and/or communicate in wired or wireless communication. By way of example, the WTRUs 102a,102b,102c,102d may be configured to transmit and/or receive wireless signals and may include User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a Personal Digital Assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like.

Communication system 100 may also include base station 114a and base station 114 b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interact with at least one of the WTRUs 102a,102b,102c,102d to facilitate access to one or more communication networks, such as the core network 106, the internet 110, and/or the network 112. For example, the base stations 114a, 114B may be Base Transceiver Stations (BTSs), node B, e node bs, home enodeb, site controllers, Access Points (APs), wireless routers, and the like. Although the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

The base station 114a may be part of the RAN 104, which RAN 104 may also include other base stations and/or network elements (not shown) such as site controllers (BSCs), Radio Network Controllers (RNCs), relay nodes, and the like. Base station 114a and/or base station 114b may be configured to transmit and/or receive wireless signals within a particular geographic area, which may be referred to as a cell (not shown). A cell may also be divided into cell sectors. For example, the cell associated with base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, one for each sector of the cell. In another embodiment, the base station 114a may use multiple-input multiple-output (MIMO) technology and thus may use multiple transceivers for each sector of the cell.

The base stations 114a, 114b may communicate with one or more of the WTRUs 102a,102b,102c,102d over an air interface 116, which air interface 116 may be any suitable wireless communication link (e.g., Radio Frequency (RF), microwave, Infrared (IR), Ultraviolet (UV), visible light, etc.). Air interface 116 may be established using any suitable Radio Access Technology (RAT).

More specifically, as previously described, communication system 100 may be a multiple access system and may use one or more channel access schemes such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a,102b,102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) terrestrial radio access (UTRA), which may establish the air interface 116 using wideband cdma (wcdma). WCDMA may include communication protocols such as High Speed Packet Access (HSPA) and/or evolved HSPA (HSPA +). HSPA may include High Speed Downlink Packet Access (HSDPA) and/or High Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114a and the WTRUs 102a,102b,102c may implement a radio technology such as evolved UMTS terrestrial radio access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE-advanced (LTE-a).

In other embodiments, the base station 114a and the WTRUs 102a,102b,102c may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA20001X, CDMA2000 EV-DO, temporary Standard 2000(IS-2000), temporary Standard 95(IS-95), temporary Standard 856(IS-856), Global System for Mobile communications (GSM), enhanced data rates for GSM evolution (EDGE), GSM EDGE (GERAN).

For example, the base station 114B in fig. 1A may be a wireless router, a home nodeb, a home enodeb, or an access point, and may use any suitable RAT for facilitating wireless connectivity in a local area, such as a business, home, vehicle, campus, and the like. In one embodiment, the base station 114b and the WTRUs 102c,102d may implement a radio technology such as IEEE802.11 to establish a Wireless Local Area Network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c,102d may implement a radio technology such as IEEE 802.15 to establish a Wireless Personal Area Network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c,102d may use a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE-a, etc.) to establish a pico cell (picocell) and a femto cell (femtocell). As shown in fig. 1A, the base station 114b may have a direct connection to the internet 110. Thus, the base station 114b does not have to access the internet 110 via the core network 106.

The RAN 104 may communicate with a core network 106, which may be any type of network configured to provide voice, data, application, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a,102b,102c,102 d. For example, the core network 106 may provide call control, billing services, mobile location-based services, prepaid calling, internetworking, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in fig. 1A, it is to be understood that the RAN 104 and/or the core network 106 may communicate directly or indirectly with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to connecting to the RAN 104, which may employ E-UTRA radio technology, the core network 106 may also communicate with other RANs (not shown) that employ GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102a,102b,102c,102d to access the PSTN 108, the internet 110, and/or other networks 112. The PSTN 108 may include a circuit-switched telephone network that provides Plain Old Telephone Service (POTS). The internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Internet Protocol (IP) in the TCP/IP internet protocol suite. The network 112 may include wired and/or wireless communication networks owned and/or operated by other service operators. For example, the network 112 may include another core network connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102a,102b,102c,102d in the communication system 100 may include multi-mode capabilities, i.e., the WTRUs 102a,102b,102c,102d may include multiple transceivers for communicating with different wireless networks over different communication links. For example, the WTRU102c shown in fig. 1A may be configured to communicate with a base station 114a using a cellular-based radio technology and to communicate with a base station 114b using an IEEE802 radio technology.

Figure 1B is a system diagram of an exemplary WTRU 102. As shown in fig. 1B, the WTRU102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a Global Positioning System (GPS) chipset 136, and other peripherals 138. It is to be appreciated that the WTRU102 may include any subset of the elements described above while remaining consistent with the above embodiments.

The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a Digital Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of Integrated Circuit (IC), a state machine, or the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functions that enable the WTRU102 to operate in a wireless environment. The processor 118 may be coupled to a transceiver 120, which transceiver 120 may be coupled to a transmit/receive element 122. Although processor 118 and transceiver 120 are depicted in fig. 1B as separate components, it will be appreciated that processor 118 and transceiver 120 may be integrated together into an electronic package or chip.

Transmit/receive element 122 may be configured to transmit signals to a base station (e.g., base station 114a) or receive signals from a base station (e.g., base station 114a) over air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive, for example, IR, UV, or visible light signals. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and receive both RF signals and optical signals. It should be appreciated that transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

Furthermore, although transmit/receive element 122 is depicted in fig. 1B as a single element, WTRU102 may include any number of transmit/receive elements 122. More particularly, the WTRU102 may use MIMO technology. Thus, in one embodiment, the WTRU102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

Transceiver 120 may be configured to modulate signals to be transmitted by transmit/receive element 122 and to demodulate signals received by transmit/receive element 122. As described above, the WTRU102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11.

The processor 118 of the WTRU102 may be coupled to and may receive user input data from a speaker/microphone 124, a keyboard 126, and/or a display/touchpad 128 (e.g., a Liquid Crystal Display (LCD) unit or an Organic Light Emitting Diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. Further, the processor 118 may access information from, and store data in, any type of suitable memory, such as non-removable memory 130 and/or removable memory 132. The non-removable memory 130 may include Random Access Memory (RAM), Read Only Memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a Subscriber Identity Module (SIM) card, a memory stick, a Secure Digital (SD) memory card, and the like. In other embodiments, the processor 118 may access data from and store data in memory that is not physically located on the WTRU102, such as on a server or home computer (not shown).

The processor 118 may receive power from the power source 134 and may be configured to distribute power to other components in the WTRU102 and/or control power to other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (nickel cadmium (NiCd), nickel zinc (NiZn), nickel metal hydride (NiMH), lithium ion (Li-ion), etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to a GPS chipset 136, which the GPS chipset 136 may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of signals received from two or more neighboring base stations. It is to be appreciated that the WTRU102 may acquire location information by any suitable location determination method while being consistent with an embodiment.

The processor 118 may also be coupled to other peripherals 138, which peripherals 138 may include one or more software and/or hardware modules that provide additional features, functionality, and/or a wireless or wired connection. For example, the peripheral devices 138 may include accelerometers, electronic compasses (e-compass), satellite transceivers, digital cameras (for photos or video), Universal Serial Bus (USB) ports, vibration devices, television transceivers, hands-free headsets, Bluetooth^○RA module, a Frequency Modulation (FM) radio unit, a digital music player, a media player, a video game player module, an internet browser, and so forth.

Fig. 1C is a system diagram of RAN 104 and core network 106 according to an embodiment. As described above, the RAN 104 may communicate with the WTRUs 102a,102b,102c over the air interface 116 using E-UTRA radio technology. The RAN 104 may also communicate with a core network 106.

The RAN 104 may include enodebs 140a, 140B, 140c, although it should be understood that the RAN 104 may include any number of enodebs while the embodiments remain consistent. The enodebs 140a, 140B, 140c may each include one or more transceivers that communicate with the WTRUs 102a,102B,102c over the air interface 116. In one embodiment, the enode bs 140a, 140B, 140c may use MIMO technology. Thus, for example, the enodeb 140a may use multiple antennas to transmit wireless signals to the WTRU102a and to receive wireless signals from the WTRU102 a.

each of the enodebs 140a, 140B, 140c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, user scheduling in the uplink and/or downlink. As shown in fig. 1C, the enode bs 140a, 140B, 140C may communicate with each other over an X2 interface.

The core network 106 shown in fig. 1C may include a mobility management entity gateway (MME)142, a serving gateway 144, and a Packet Data Network (PDN) gateway 146. Although each of the above elements are described as being part of the core network 106, it should be understood that any of these elements may be owned and/or operated by an entity other than the core network operator.

MME 142 may be connected to each of enodebs 140a, 140B, 140c in RAN 104 through an S1 interface and may act as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a,102b,102c, bearer activation/deactivation, selecting a particular serving gateway during initial connection of the WTRUs 102a,102b,102c, and the like. MME 142 may also provide control plane functionality for exchanges between RAN 104 and RANs (not shown) that use other radio technologies (e.g., GSM or WCDMA).

The serving gateway 144 may be connected to each of the enodebs 140a, 140B, 140c in the RAN 104 through an S1 interface. The serving gateway 144 may generally route and forward user data packets to the WTRUs 102a,102b,102c or route and forward user data packets from the WTRUs 102a,102b,102 c. The serving gateway 144 may also perform other functions such as anchoring the user plane during inter-enodeb handovers, triggering paging when downlink data is available to the WTRUs 102a,102B,102c, managing and storing the context of the WTRUs 102a,102B,102c, and so on.

The serving gateway 144 may also be connected to a PDN gateway 146, which PDN gateway 146 may provide the WTRUs 102a,102b,102c with access to a packet-switched network (e.g., the internet 110) to facilitate communications between the WTRUs 102a,102b,102c and IP-enabled devices.

The core network 106 may facilitate communication with other networks. For example, the core network 106 may provide the WTRUs 102a,102b,102c with access to a circuit-switched network (e.g., the PSTN 108) to facilitate communications between the WTRUs 102a,102b,102c and conventional landline communication devices. For example, the core network 106 may include, or may communicate with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that interfaces between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a,102b,102c with access to other networks 112, which other networks 112 may include other wired or wireless networks owned and/or operated by other service providers.

Other networks 112 may also be connected to an IEEE802.11 based Wireless Local Area Network (WLAN) 160. WLAN 160 may include an access router 165. The access router may comprise a gateway function. The access router may communicate with a plurality of Access Points (APs) 170a, 170 b. Communication between the access router 165 and the APs 170a, 170b may be via wired ethernet (IEEE 802.3 standard) or any type of wireless communication protocol. The AP 170a may communicate wirelessly with the WTRU102 d over an air interface.

A plurality of bands of 6GHz or more including, for example, 10GHz and 15GHz bands (cmW bands) and 28GHz, 39GHz, 60GHz, and 73GHz bands (mmW bands) have been evaluated. These higher frequency bands may be allocated, for example, as licensed, lightly licensed, and unlicensed spectrum.

The high frequency band, as described above, may be deployed within various cellular network configurations depending on the spectrum allocation and its propagation characteristics. For example, mmW frequencies may be used within a homogeneous network with mmW individual macro base stations, micro base stations, and small cell base stations (scmbs). The heterogeneous network may include a mmW individual small cell network with Long Term Evolution (LTE) macro and/or pico networks overlaid (overlay) below 6 GHz. Within this network, network nodes may be connected to frequencies above 6GHz (e.g., mmW systems) and below 6GHz (e.g., 2GHz LTE systems). This type of connection may be referred to as a dual connection. In an embodiment, carrier aggregation may be applied to combine carriers above 6GHz (e.g., mmW carriers) with carriers below 6GHz (e.g., 2GHz LTE carriers). The embodiments described herein are applicable to any cellular deployment above 6 GHz.

Waveforms such as OFDM, wideband Single Carrier (SC), SC-OFDM, general OFDM, Filter Bank Multi-Carrier (FBMC), or Multi-Carrier-CDMA (MC-CDMA) may be used for systems above 6 GHz. The waveforms may have different peak-to-average power (PAPR) performance, sensitivity to transmitter non-linearity, Bit Error Rate (BER) performance, resource channelization, and implementation complexity. Although the frame structure may depend on the applied waveform, its specifications may also be adjusted to meet system requirements above 6 GHz. For example, to achieve very low latency, higher frequency cellular systems may have a subframe length of 100 us.

Fig. 2 is a diagram 200 of an exemplary OFDM frame structure for an exemplary 1GHz system bandwidth. In the example shown in fig. 2, the OFDM-based frame structure has a subcarrier spacing of 300kHZ and a corresponding symbol length of 3.33 mus. Considering that Cyclic Prefix (CP) length may be spread across the entire length of the channel time to eliminate inter-symbol interference, with respect to T for 3.33 mus_symbolAn example of a CP of (A) may be, T _symbo1/4, i.e., at 0.833 μ s. This exemplary parameter configuration (numerology) may be used for system bandwidth ranges above 6GHz (e.g., from 50MHz to 2GHz) with corresponding Fast Fourier Transform (FFT) lengths.

Fig. 3 is a diagram 300 of an exemplary single carrier frame structure for an exemplary 2GHz system bandwidth. The frame structure shown in fig. 3 is based on the use of a single carrier over the entire system bandwidth, which in the example shown is 2GHz, but which may range, for example, from 50MHz to 2 GHz. In the case of 1024FFT, the sampling frequency may be 1.536 GHz. A subframe may be 100 μ s and have 150 SC blocks. Each block may be 1024 symbols, which may be used for synchronization, reference, control, data, cyclic prefix, or other system purposes.

Systems above 6GHz (such as cmW systems or mmW systems) may employ any of the waveforms and frame structures, or any combination of waveforms and frame structures, described above. The embodiments described herein may be applied to all or any of these waveforms and frame structures.

Systems above 6GHz may use Frequency Division Duplexing (FDD), Time Division Duplexing (TDD), Space Division Duplexing (SDD), or any combination thereof, in conjunction with half-duplex or full-duplex mechanisms. A full duplex FDD system may use duplex filters to allow simultaneous downlink and uplink operation at different frequencies separated by a duplex distance. A half-duplex FDD system may not use a duplex filter because downlink and uplink operations may occur at different times within its dedicated frequency. A TDD system may have downlink and uplink operations at different times but at the same frequency. SDD systems (e.g., in beamforming systems) may enable network nodes to transmit and receive on the same frequency and time instant, but in different outward and inward spatial directions.

Systems above 6GHz may use, for example, FDMA, TDMA, Spatial Division Multiple Access (SDMA), Code Division Multiple Access (CDMA), non-orthogonal multiple access (NOMA), or any combination thereof. FDMA, TDMA, SDMA, and CDMA may be applied in an orthogonal manner to avoid interference.

Multiple network nodes may be assigned to use different frequency resources within an FDMA system simultaneously or to access system frequency resources at different times within a TDMA system. Furthermore, in a CDMA system, network nodes may access the same frequency resources at the same time, but use different codes. SDMA systems may assign spatial resources to network nodes to operate on the same frequency, time, and code resources. For example, in a beamforming network, a WTRU may use different beams.

In a NOMA system, multiple network nodes may be assigned resources that overlap or are the same in the frequency, time, code or spatial domain, but additional mechanisms may be applied to remove interference due to non-orthogonal use of resources between users. For example, two WTRUs may be far apart from each other and their path loss differences to the base station may be large. They may be assigned the same frequency resources within the same subframe, but with very different transmission formats. Superposition coding and Successive Interference Cancellation (SIC) receivers may be used in a WTRU to remove a received signal for another.

Systems above 6GHz (such as cmW systems or mmW systems) may apply any of the above-described duplexing schemes, multiple access, or a combination thereof. The embodiments described herein are applicable to all of these duplex and multiple access schemes.

Systems above 6GHz may have multiple physical channels and signals for various system purposes. Some signals may be used for multi-system processes. For example, the synchronization signal may be predefined and may be used for cell timing/frequency synchronization. The synchronization signal may be transmitted according to a predefined periodicity. Within a beamforming system (such as cmW or mmW networks), signals may provide beam timing and assistance in the frequency acquisition process. The Physical Broadcast Channel (PBCH) may carry broadcast information, such as cell-specific System Information (SI). The downlink interfering signal may be a predefined sequence that is transmitted to enable various system processes such as channel estimation for control channels, channel announcement measurements, timing and frequency fine tuning, and system measurements. There may be different types of reference signals. For example, within a beamforming system (such as cmW or mmW networks), downlink reference signals may be used for, for example, beam acquisition, beam pairing, beam tracking, beam switching, and beam measurement.

The Physical Downlink Control Channel (PDCCH) may carry all data-related control information to, for example, properly identify, demodulate, and decode the associated data channel. The physical downlink data channel may carry payload information in the form of a Medium Access Control (MAC) Protocol Data Unit (PDU) from the MAC layer. The resource allocation for this channel may be carried within scheduling information within the PDCCH. The data demodulation reference signal may have symbols that may be transmitted for channel estimation of a downlink control or data channel. These symbols can be placed together with the associated control or data symbols in the time and frequency domain according to a predefined pattern (pattern), ensuring correct insertion and reconstruction of the channel.

Uplink reference signals may be used for uplink channel sounding and uplink system measurements, for example. Within a beamforming system (such as cmW or mmW networks), uplink reference signals may be used for, for example, uplink beam acquisition, uplink pairing, beam tracking, beam switching, and beam measurement. The Physical Random Access Channel (PRACH) may carry a predefined sequence related to the random access procedure. The Physical Uplink Control Channel (PUCCH) may carry uplink control information such as channel state information, data acknowledgements, and scheduling requests. The physical uplink data channel may carry payload information in the form of MAC PDUs from the WTRU MAC layer. The resource allocation for the channel may be conveyed within the PDCCH. The data demodulation reference signal may have symbols that may be transmitted for channel estimation of an uplink control or data channel. These symbols may be placed together with the associated data symbols in the time and frequency domain according to a predefined pattern, ensuring correct insertion and reconstruction of the channel.

Systems above 6GHz (such as cmW systems or mmW systems) may deploy the above signals and channels. The embodiments described herein are applicable to all of these physical signals and channels.

In systems above 6GHz (such as cmW systems or mmW systems), beamforming may be important. For example, fault studies conducted in urban areas using steerable 100 bandwidth and 24.5-dBi horn antennas at 28GHz and 38GHz bands have shown that consistent coverage can be achieved over cell radii of up to 200 meters.

It may currently be assumed that LTE WTRUs have omni-directional beam patterns and may perceive superimposed channel impulse responses throughout the angular domain. Thus, aligned beam pairing (e.g., at mmW frequencies) may provide additional degrees of freedom in the angular domain compared to current LTE systems.

A Phase Antenna Array (PAA), which may have an element spacing of, for example, 0.5 λ, may be used for beamforming, and the phase antenna may apply different beamforming algorithms, such as full digital beamforming, analog beamforming (e.g., for one or more Radio Frequency (RF) chains), and hybrid beamforming.

Fig. 4 is a schematic diagram 400 of an exemplary PAA for full digital beamforming. A fully digital beamforming method, such as that shown in fig. 4, may have a dedicated RF chain that includes RF processing and analog-to-digital conversion (ADC) for each antenna element. The signals processed by each antenna element can be individually controlled in phase and amplitude to optimize channel capacity. Thus, for full digital beamforming, the configuration may have the same number of RF chains and ADCs as antenna elements. While providing very high performance, fully digital beamforming may result in high cost and complexity for implementation and may result in high power consumption during operation.

Fig. 5 is a diagram 500 of an example of analog beamforming with one PAA (which contains one RF chain for multiple antenna elements). In the example shown in fig. 5, each antenna element is connected to a phase shifter for setting the weights for beamforming and steering. The number of RF chains implemented and the power consumption can be significantly reduced.

The phase shifting and combining may be implemented in different stages, such as an RF stage, a Baseband Beamforming (BB) analog stage, or a Local Oscillator (LO) stage. One example is a single beam analog configuration that can operate one beam at a time, where the single beam can be placed, for example, in the strongest angular direction, such as the line-of-sight (LOS) path acquired by beam measurements. The wide beam pattern may cover a range of angular directions at the expense of reduced beamforming gain.

Hybrid beamforming may combine digital precoding with analog beamforming. The analog beamforming may be performed on phased array antenna elements, each associated with a phase shifter and all connected to one RF chain. The digital precoding may be applied to the baseband signal of each RF chain.

Examples of system parameters for hybrid beamforming may include number of data streams (NDATA), number of RF chains (NTRX), Number of Antenna Ports (NAP), Number of Antenna Elements (NAE), and Number of Phase Antenna Arrays (NPAA). The configuration of these parameters may affect system functionality and performance, as will be described in more detail below.

Fig. 6 is a diagram 600 of an example of analog beamforming with one PAA and two RF chains. In this embodiment, one antenna port may carry a beamforming reference signal uniquely associated with the antenna port, which may be used to identify the antenna port. In the example shown in fig. 6, one PAA of size 4x 4 is connected to two RF chains, and each RF chain has a set of 16 phase shifters. The PAA may form two narrow beam patterns within +45 ° and-45 ° coverage in the azimuth plane. In this configuration, N_PAA<N_AP＝N_TRX<N_AE。

Fig. 7 is a schematic diagram 700 of an example of analog beamforming with two PAAs and two RF chains. In the example shown in fig. 7, each PAA has a dedicated RF chain (i.e., N)_PAA＝N_AP＝N_TRX≤N_AE). This configuration may allow spatial independence between two simultaneous beams by placing PAAs in different orientations (e.g., in azimuth). The aligned PAA arrangement may provide a larger coverage of the aggregation. The examples shown in fig. 6 and 7 with two RF chains can apply Multiple Input Multiple Output (MIMO) with two data streams.

Fig. 8 is a schematic diagram 800 of an example of analog beamforming with two PAAs and one RF chain. In the embodiment shown in fig. 8, multiple PAAs may be connected to a single RF chain (i.e., N) using a switch_AE>N_PAA>N_AP＝N_TRX). Each PAA may form a narrow beam covering a range of +45 ° to-45 ° in the azimuth plane. They may be individually oriented so that a single beam network node may have good coverage by using beams in different directions at different times.

Systems above 6GHz (such as cmW systems or mmW systems) may apply different beamforming techniques, such as analog, hybrid, and digital beamforming described above. The embodiments described herein are applicable to all of these beamforming techniques.

To overcome the high path loss at the 6GHz frequency, transmit and/or receive beamforming may be applied to control channel transmission/reception. The resulting beamformed link may be considered spatially filtered and may limit the WTRU's reception of the angle-of-arrival path. Legacy cellular systems rely on omni-directional or cell-wide beams for control channel transmission, and in these systems the placement of the control channels is well defined from the WTRU perspective (e.g., in the control area). However, at higher frequencies, each base station may have multiple control channel beams to cover the cell, and the WTRU may be able to receive only a subset of them. Embodiments described herein may provide methods and apparatus for identifying candidate control channel beams and their locations within a subframe structure.

Millimeter wave base stations (mbs) and WTRUs in a beamforming system may have a diverse set of capabilities, such as different numbers of Radio Frequency (RF) chains, different beamwidths, or different numbers of Phase Antenna Arrays (PAAs). An mB with multiple RF chains may transmit multiple control channel beams within the same symbol, and a WTRU with multiple RF chains may receive the same control symbol by using multiple receive beam patterns. An mB with one RF chain may need to multiplex control channel beams in the time domain (e.g., different symbols and/or different subframes). A mB with multiple RF chains may multiplex control channel beams in time and space domain. Embodiments described herein may provide a framework for beamforming control channel design that may support varying capabilities of mbs and WTRUs and may support time and spatial multiplexing of control channel beams.

Long Term Evolution (LTE) common reference signal design assumes cell-wide transmission. For multi-beam systems, modifications to the reference signal design may be required to discover, identify, measure, and decode each control channel beam. In a multi-beam system, interference between beams may degrade the overall cell capacity. Embodiments described herein may provide additional mechanisms to mitigate inter-beam interference for intra-cell and inter-cell scenarios.

As described above, beamforming may be required at both the transmitter and the receiver to achieve the high throughput requirements of a 5G system. Embodiments described herein may provide the capability to support WTRUs having a wide variety of beamforming capabilities. Further, embodiments described herein may provide WTRU-assisted, network-controlled procedures for narrow beam pairing on the Uplink (UL) and Downlink (DL).

The directional nature of mmW links may mean that the number of Radio Link Failure (RLF) events may increase compared to LTE links for the same inter-small cell distance (ISD) and WTRU speed. In addition to mobility, changes to WTRU orientation may also cause RLF events when mmW links are used. Further, mmW links may be more likely to be blocked due to changes in the environment (such as due to moving people and buses). Embodiments described herein may provide methods and apparatus for a WTRU to detect and recover from beam failures. Further, a connectivity concept may be provided that may help address issues related to beamforming and may make mmW carriers available for cellular access.

Basic building blocks for beamforming control of a beamforming system may include a subframe structure, a beamforming control channel, a beamforming data channel, a data region with one or more beamforming data channels, a control region with one or more beamforming control channels, and a gap. Each of the building blocks will be described in detail below.

With regard to the subframe structure, each subframe may include a plurality of symbols, one or more of which may be used to transmit or receive one or more control signals, control channels, control information, and/or data channels. When referenced, a subframe may be used interchangeably with a scheduling time interval, time slot, or predefined time unit.

With respect to beamforming control and data channels, a control channel or a data channel may be transmitted by using a particular radiation pattern or beam. Each control or data channel beam may be associated with one or more of: a unique reference symbol, a steering vector, a scrambling code, an antenna port, a time resource, a code resource, a spatial resource, a frequency resource, or a control channel identification. Each mB or cell may transmit multiple beamforming control and/or data channels. In some embodiments, the beamforming control and/or data channels may be multiplexed in time.

With respect to a data region having one or more beamformed data channels, one or more symbols within a subframe (in which the data channels are transmitted) may be referred to as a data region. Within a subframe, a data region may include multiple data channel beams that may be multiplexed in time. For example, a data signal within a particular beam may occupy one or more symbols, while the remaining symbols within the same subframe may be used to transmit data channels in other beams. Each data channel beam within the data region may have a variable beamwidth. In some embodiments, the WTRU's maximum data channel beamwidth may have the same width as its control channel beamwidth. One WTRU may receive one or more data channels transmitted using one or more beams or beamwidths within a subframe or across different subframes. Multiple WTRUs may be time multiplexed within a subframe, within the same data channel beam, or across different data channel beams. The smallest schedulable time resource within a subframe may be a symbol or a group of symbols. The scheduling granularity may be smaller than a subframe (e.g., a new Downlink Control Information (DCI) format may carry information at the symbol level or symbol group).

With respect to a control region having one or more beamformed control channels, one or more symbols within a subframe (in which the control channels are transmitted) may be referred to as a cell-specific control region. Within a subframe, a cell-specific control region may contain multiple control channel beams multiplexed in time. One or more symbols within a subframe in which a control channel for a particular beam is transmitted may be referred to as a beam-specific control region. In some embodiments, a control region may refer to a cell-specific control region and/or a beam-specific control region. The control region size may be fixed or flexibly variable. In some embodiments, the control region and the data region may overlap, and one or more symbols may carry the control channel and the data channel multiplexed in the frequency, code, or spatial domain.

With respect to gaps, they may be placed between two consecutive symbols carrying transmissions with different beam directions, radiation patterns, or steering vectors. When referred to herein, a gap may be used interchangeably with a switching period, a guard period, a silence period, a transmission absence period, or a Discontinuous Transmission (DTX) period. Depending on the arrangement, different gap types may be identified, including, for example, a gap between two control symbols or groups of control symbols, a gap between two data symbols or groups of data symbols, and a gap between a control symbol and a data symbol (e.g., between a last control symbol and a first data symbol or vice versa).

Different gap types may be preconfigured with different durations. The same gap type may be preconfigured with different durations within different subframes. The gap may be selectively arranged between two consecutive symbols transmitted with different radiation patterns, beam patterns, directions or channel types. The gap may be selectively arranged between the control symbol and the data symbol. The gaps within the same subframe may have different durations. Gaps may or may not exist within all subframes. The gaps may be arranged between control symbols and may not be arranged between data symbols, or vice versa. Within the control region or the data region, gaps may be selectively arranged between subsets of symbols.

The gaps may be defined from the WTRU perspective. The WTRU may not be required to receive on the Downlink (DL) during the gap period (e.g., the gap between the control symbols and the data symbols for a particular WTRU). The WTRU may use the gap period to decode a control channel that may be received before the start of the gap period. The WTRU may use the gap period to switch its receive beam or apply a new steering vector (which may be different from the receive beam or steering vector used to receive the downlink control channel) to receive the downlink data channel. The WTRU may use the gap period (e.g., for a particular WTRU, the gap between data symbols or between groups of data symbols) to switch its receive beam or apply a new steering vector (which may be different from the receive beam or steering vector used to receive the previous downlink data channel in the same or different subframe) to receive the downlink data channel.

A cell (such as a mmW cell or a 5G cell) may be defined by one or more transmissions sharing at least one discovery signal characteristic. In an embodiment, the one or more transmissions sharing the at least one discovery signal characteristic may be restricted to a spatial domain. The physical transmission may originate from a plurality of transmission points. Discovery signals between different physical transmissions may be multiplexed in the time, frequency, code, and/or spatial domains. In an embodiment, a cell may be defined as a collection of beams from one or more transmission points. Each transmission point may be associated with one or more cells, wherein only a subset of beams from the transmission point may be associated with each cell. The 5G cell may be characterized by virtual-less properties and/or elastic properties.

The virtual attribute may refer to a cell being logical and not bound to a physical transmission point. The transmission points associated with the cell may be considered to form a cluster.

In conventional cellular architectures, hard edges/boundaries are created between adjacent cells. WTRUs located at these edges may experience low throughput, high interference, dropped calls, or dropped data due to frequent handovers. Cell densification may be a step to improve the air capacity, but cell densification may also result in more edges per unit area.

The virtual attributes may be extended to create a cell from the WTRU's perspective that is edge-free. Dynamically coordinated transmission may enable a WTRU-center-cell, where the WTRU may always receive the best possible signal-to-interference-and-noise ratio (SINR). Cell densification may also lead to increased mobility events (e.g., handovers), which may generate data interruptions. The virtual attributes may be used to create a WTRU-specific mobile cell, where a cell follows the WTRU and mobility may be handled through inter-node coordination with minimal feedback (e.g., measurement reports) from the WTRU.

Each mB or DL beam from the mB may be logically associated with multiple virtual cells, where each cell may be WTRU or service specific. This may be enabled by transmitting multiple discovery signals on the same beam separated in frequency or time.

The elasticity property of a cell may refer to its flexibility in adapting the coverage to meet a predefined criterion (criterion) which may include one or more of the following: inter-cell interference reduction, adaptive coverage adjustment based on WTRU distribution (e.g., increased capacity where there is a higher WTRU density), and time-dependent coverage adaptation (e.g., based on time, day of week, etc.). The elastic properties can be used to provide self-healing capabilities in ultra-high density deployments with a wide range of coverage. For example, if one cell (cell 2) loses power, another cell (cell 1) may temporarily increase its coverage area to serve WTRUs within cell 2. For directional transmissions (such as directional transmissions in higher frequencies), spatial coverage adaptation may be used to overcome the blockage. In addition, flexible coverage adaptation may be considered as inter-cell interference coordination within the airspace. Small cell on/off may be considered as a new energy saving method within ultra high density deployments. By selectively turning off directional transmissions in a beamformed cell, rather than turning off these directional transmissions for the entire cell, finer granularity control in terms of energy efficiency may be provided.

Fig. 9 is a diagram 900 illustrating an example of elastic properties within an ultra-high density deployment. Four examples are shown in fig. 9. In example 908a, the three mbs 902, 904, and 906 may operate in omni-directional coverage. The mB may dynamically learn the interference patterns (e.g., from WTRU feedback) and self-organize itself to optimize services for a given network topology, WTRU distribution, and service requirements, such as examples 908 and 908 c. As example 908c is for the mB 904, in the event of extreme congestion or sudden failure, the mB may perform self-healing to adapt their coverage area and serve WTRUs previously served by the mB 904. Thus, by using self-healing, sudden coverage holes (holes) can be corrected by a smooth degradation of the capacity throughout the region.

In an embodiment, a WTRU may be associated with more than one mB. In this embodiment, in the downlink, the WTRU may acquire DL time synchronization for each mB. Further, the WTRU may determine the best beam pair to receive downlink transmissions from multiple cells. This beam pairing may be mB-specific (i.e., different mbs may have different effective receive beams at the WTRU). The multiple mbs to which the WTRU is connected may form a logical cluster. Coordination between clusters may be centralized or decentralized.

In the uplink, the WTRU may transmit random access or other reference signals in the UL so that the WTRU may perform uplink time synchronization with multiple mbs. Additionally, this UL transmission may be beamformed so that a preferred UL beam pairing may be established between the WTRU and the mB. This beam pairing may be mB-specific (i.e., different mbs may have different preferred WTRU transmit beams).

Partial WTRU contexts may be stored within multiple mbs. The WTRU context may include semi-static parameters and dynamic parameters. The semi-static parameters may include, for example, a WTRU ID, active radio bearer information, and/or WTRU capability information. The dynamic parameters may include layer 2(L2) context (e.g., automatic repeat request (ARQ) context and/or Packet Data Convergence Protocol (PDCP) context, Radio Resource Control (RRC) context, security configuration, mB-specific DL beam ID, and/or Channel State Information (CSI)). The dynamic parameters may be periodically synchronized with all mbs within a WTRU-specific cluster.

DL data is available at one or more mbs forming a cluster of WTRUs. For example, data from a Serving Gateway (SGW) may be multicast to mbs within the cluster. Additionally or alternatively, the anchor mB may receive the data stream from the SGW and may then broadcast the data to mbs within the cluster. Additionally or alternatively, within a dual connectivity context, the macro eNB may broadcast the data to one or more mbs within the cluster.

In ultra-high density deployments, the WTRU may be configured to search for a backup (backup) mB. The trigger for the backup mB search may depend on the serving mB signal quality. The backup mB search may rely on, for example, one or more of: a periodic timer expiration, a number of discovered standby mbs, and WTRU capabilities (e.g., number of RF chains or number of PAAs). The value of the periodic timer may be broadcast within System Information (SI).

The radio link between the WTRU and the network may be characterized by a beam pair formed by a transmit beam and a receive beam. In some embodiments, the beam pairing on the DL may be different from the beam pairing used within the UL, and vice versa. Each beam may be identified by a reference signal, a serial number, a logical antenna port, and/or any other unique identification. The two beams within a beam pair may have the same beam width. In some embodiments, a WTRU may be connected to multiple base stations and a separate beam pair may be defined for each radio link.

Different levels of beam pairing may be defined, including, for example, wide beam pairing, narrow beam pairing, and wide-narrow beam pairing. In embodiments, the WTRU may determine one or more preferred DL beams during a cell search and/or synchronization procedure, such as during reception of a synchronization signal, a PBCH signal, and/or a system information broadcast. The network may determine one or more preferred UL beams during a random access or sounding procedure. Once the random access procedure is completed, the WTRU and the network may establish a beam pairing. A WTRU in connected mode may receive a command from the network to update beam pairing and, optionally, may agree to spare beam pairing, perform beamforming transmission for UL beam training on the UL, and transmit and/or receive data channels on specific narrow beams (which may be designated via, for example, scheduling grants or higher layer messages).

In addition to beamforming at the mB, beamforming at the WTRU is needed to compensate for the additional path loss at higher frequencies. Methods and apparatus for UL beamforming and scheduling are described in detail below.

Fig. 10 is a flow chart 1000 of an exemplary method of wave velocity shaping and scheduling. In the example shown in fig. 10, the WTRU1002 performs a RACH procedure with the mB1004 (1006). As described in more detail below, the WTRU1002 may perform random access using multiple transmit beams or steering vectors to obtain an initial coarse estimate of the preferred UL wide beam and timing advance. Thereafter, the WTRU1002 may enter an RRC connected mode (1008). The WTRU1002 and mB1004 may further perform UL narrow beam pairing procedures to determine the best beam pairing for high throughput data transfer and to reduce interference with the co-existing link.

Once in RRC connected mode, the WTRU1002 may transmit beamforming capability information (e.g., within a WTRU capability report) to the mB1004 (1010). As described in detail below, the WTRU1002 may autonomously transmit a beamforming capability message, e.g., after entering an RRC connected state, or the mB1004 may request beamforming capability information via a request message. The WTRU1002 and mB1004 then engage in a beam pairing procedure 1012, which may involve a beam pairing command (1014) and beam pairing response (1016) exchange between the WTRU1002 and mB 1004.

In the example shown in fig. 10, the mB1004 may trigger a beamforming reference signal from the WTRU1002 (1018). Further, in the example shown in fig. 10, in response to the trigger (1018), the WTRU1002 may map a reference signal configuration or sequence to multiple transmit beams (1020) and transmit a reference signal on each beam (1022,1024,1026). The following embodiments will describe in detail different procedures for transmitting beamforming reference signals. The mB1004 may grant resources within the DCI for triggering UL reference signal transmission (1028), and at the same time may provide an explicit reference signal sequence to be used for transmission on the resources. As described in detail below, mB1004 may also include a 1-bit command indicating a link (linkage) of the reference signal sequence.

The WTRU may perform random access using multiple transmit beams or steering vectors to obtain an initial coarse estimate of the preferred UL wide beam and timing advance. The WTRU and mB may further perform UL narrow beam pairing procedures to determine the best beam pairing for high throughput data transfer and to reduce interference with the co-existing link. Embodiments described herein may be used for narrow beam pairing and/or broad beam pairing or re-pairing. In the embodiments described below, the UL reference signal transmission may be replaced with a random access preamble transmission.

The WTRU may be configured with dedicated UL resources for the UL beam pairing procedure. In an embodiment, the resource configuration may depend on WTRU capabilities. WTRU capabilities may include one or more of: the total number of TX (transmit) beams supported by the WTRU (which may include TX beams from multiple PAAs at the WTRU), the number of narrow TX beams (e.g., within spatial coverage) associated with each Random Access Channel (RACH) beam, the number of narrow TX beams (e.g., within spatial coverage) associated with the current UL control channel beam, the quantized beamwidth supported by the WTRU, the number of PAAs within the WTRU, the number of RF chains within the WTRU, and the type of beamforming technology used by the WTRU (e.g., analog, digital, or hybrid).

In embodiments, WTRU capabilities may be represented by different device classes, such as low class, medium class, or high class. The WTRU category may determine the UL beamforming resource allocation.

The WTRU may transmit its beamforming capabilities via higher layer signaling messaging (e.g., by using RRC messages). The WTRU may autonomously transmit the message after entering the RRC connected state, or the mB may request the capabilities via a request message. In an embodiment, different groups of random access resources may be associated with WTRU categories (e.g., low, medium, or high). The WTRU may implicitly indicate the device class through selection of a random access resource group. In other embodiments, the mB may always configure a predefined set of resources for UL beam pairing regardless of WTRU capabilities. In some cases, the WTRU may only need to indicate that it is capable of transmitting a narrower beam than the UL beam used for random access. The 1-bit information may be implicitly indicated via the selection of the random access preamble. Thereafter, the mB may further trigger a capability request message to acquire the number of UL narrow beams supported by the WTRU.

The WTRU may use the dynamic indication to signal a change in its TX beam capabilities (e.g., self-blockage due to, for example, hand, head, or body). The WTRU may be configured to transmit beamforming reference signals on UL resources configured for beam pairing. This configuration may include two portions, such as a semi-static portion and a dynamic portion.

The semi-static UL beam pairing resource configuration may be cell-specific, mB-RX-beam-specific, and/or WTRU-specific. The WTRU may receive the semi-static configuration via a System Information Block (SIB) and/or a WTRU-specific RRC configuration. The semi-static UL beam pairing resource configuration may include beamforming reference signal sequences and cyclic shifts, which may depend on, for example, RX beams at mB, WTRU ID, cell ID, subframe number, or symbol number. The semi-static UL beam pairing resource configuration may also or alternatively include a frequency domain resource configuration, which may include, for example, a bandwidth, a starting RB location, a hopping configuration, or a transmission comb (comb) factor. The frequency domain resources may depend on, for example, system bandwidth or WTRU density. The semi-static UL beam-pair resource configuration may also or alternatively include a time-domain resource configuration, which may include, for example, a subframe, a symbol within a subframe to be used for UL beam-pair reference signals, a periodicity, or a repetition factor. In an example, the base time domain resource may be configured, and the WTRU may then determine the subsequent resource by a pre-configured offset/period.

One or more symbols within a subframe may be allocated for UL beam-pair reference signal transmission. For example, a WTRU may transmit multiple UL beam pairing reference signals within one subframe using the same transmit beam.

The WTRU may transmit the UL beam pairing reference signal based on, for example, an mB command or a pre-configured criterion. The WTRU may receive a trigger to transmit the UL beam pair reference signal in a number of different ways. For example, the mB may or may not dynamically schedule UL beam-pair reference signal transmissions with data within the same UL subframe. The resources for UL beam-pair reference signal transmission may be allocated similar to UL data transmission. This may provide higher granularity in terms of frequency and time domain resources within a subframe. A plurality of symbols within a subframe may be allocated for UL beam-pair reference signal transmission. Alternatively, the mB may use only 1-bit field within the DCI to turn on/off beam pair reference signal transmission. The detailed resource configuration information may be signaled as having precedence over triggering the semi-static configuration of the DCI. The DCI embodiments may be used for, for example, one-time beam-reference signal transmission.

Another example of how a WTRU receives a trigger to transmit an UL beam pair reference signal is to use MAC control messages for activating and deactivating UL beam pair reference signal transmission. Similar to the DCI embodiment, the resource allocation information may be semi-statically configured. Once activated, the WTRU may transmit UL beam pairing reference signals according to a predefined period until deactivated by the mB. For another example, the WTRU may receive a trigger to transmit an UL beam pairing reference signal based on a multi-beam PDCCH order or based on a Random Access Response (RAR) following the PDCCH order that triggers the WTRU to perform UL transmission of multiple reference signals using multiple time multiplexed TX beams.

Another example of how a WTRU may receive a trigger to transmit a UL beam pairing reference signal is that the WTRU may be configured to transmit the UL beam pairing reference signal while in RRC connected mode. This configuration may be provided via higher layer signaling (e.g., RRC message or using RAR), which may include configuration for subsequent UL reference signal transmissions. The WTRU may stop transmitting the UL beam pairing reference signals when it leaves the connected mode.

Another example of how a WTRU receives a trigger to transmit a UL beam pairing reference signal is that the WTRU may trigger the UL beam pairing reference signal based on a pre-configuration event. Such an event may include one or more of: the number of negative acknowledgements for UL data transmissions is above a predefined threshold, rotation or motion detection based on the WTRU (e.g., via an accelerometer or gyroscope) is above a predefined threshold, and changes within the serving DL beam (e.g., control beam or narrow data beam). In an embodiment, the WTRU may transmit an UL beam pairing request on an UL control channel based on one or more of these pre-configuration events.

The WTRU may periodically transmit UL reference signals, scan all TX beams or a subset of TX beams, or may perform only one full scan or one transmission of a subset of TX beams. In the case of using a TX beam subset, the WTRU may autonomously select the beam subset, or the beam subset to be used may be specified via DCI, MAC, and/or RRC signaling. The TX beam may be identified by a UL reference signal ID or a beam ID. The subset may be determined based on one or more of: selecting a beam within a spatial coverage of a current UL control channel; selecting a TX beam associated with an RX beam for DL data channel reception, wherein the association may be defined by a steering vector or a value of spatial proximity; based on an angle of arrival (AoA) estimate at the WTRU; and based on previous aperiodic measurements from the mB.

In an embodiment, the WTRU may transmit only narrow beams within the coverage of the current UL wide control beam used by the WTRU. In an embodiment, the UL beamforming reference signal may be configured as a sounding reference signal.

An exemplary UL resource configuration may include information about the start of the UL resource allocation (e.g., a predefined offset by the number of subframes or TTIs), information about the periodicity T (e.g., by the number of subframes or TTIs), the number of symbols and/or symbol numbering within each subframe allocated for UL reference signal transmission, bandwidth and hopping configuration, a set of sequence numbers from S0 to SN, and a repetition factor. For sequence numbers, the starting sequence number may be S0, and the number of sequences N may be derived from the starting sequence number (e.g., the number of times the UL TX beam is transmitted before switching to the next TX beam within the sequence). For example, the starting sequence number may be a base sequence, and other sequences may be derived by cyclically shifting the base sequence. The mB may use different RX beams to receive repetitions for the same TX beam.

Given the UL resource configuration, the WTRU may associate each TX beam n with a unique sequence number Sn within a set of sequence numbers. For example, the number of TX beams supported by the WTRU may be made M. The WTRU may use the first M sequence numbers of the set if M < >, N. If M > N, the WTRU may select N beams based on a prioritization criterion. For example, the prioritization criteria may be based on spatial proximity between the current UL control beam and the selected TX beam, or may be based on WTRU-based TX beam subset selection criteria.

Starting with the first configured UL resource and the first selected beam, the WTRU may sequentially scan each of its selected TX beams with each subsequent UL resource, where each TX beam transmission may be repeated by a configured repetition factor. When the WTRU has exhausted all its selected TX beams, the WTRU may start again with the first TX beam and maintain the same scanning order each time. From the perspective of mB, there are only two possibilities for the upcoming UL reference signal transmission, either the next sequence number in the sequence or the sequence number around the starting sequence number. The WTRU may maintain a mapping between sequence numbers and TX beams for all scanning operations. The map may be used by the mB to indicate the selected beam for subsequent data or control transmission.

In an embodiment, the WTRU may associate or reset the mapping between UL reference signal sequences and TX beams under one or more of the following scenarios: when there is a change in the uplink control beam; providing an explicit indication during an uplink control beam switching procedure; there is a change in the uplink data channel beam; providing an explicit indication during an uplink data channel grant or a handover procedure; when the WTRU receives a deactivation command for UL reference signal transmission; upon receiving an explicit reset command to clear the mapping; and/or when a beam failure procedure or cell level monitoring procedure is triggered.

In WTRU-based implicit reference signal sequence number to TX beam mapping, for N < M, the network and WTRU may eventually experience a sequence number mismatch when the UL control beam is updated or when one or more TX beams cannot be received at the mB. To handle this, the WTRU may receive a reset command from the mB to invalidate the current mapping between the reference signal sequence number and the TX beam. The WTRU may then restart the process and reassign the new mapping as described above.

In an embodiment, in addition to UL reference signal transmission, the WTRU may transmit an explicit sequence number to identify the UL TX beam. The sequence number may be added to the UL reference signal transmission by adding a preamble to the UL transmission to identify a UL beam ID and/or assigning a beam ID to a TX beam according to the WTRU implementation with the one-to-one mapping restriction.

In other embodiments, the mB may assign a specific reference signal sequence to the upcoming WTRU UL reference signal transmission. The reference signal sequences may be signaled along with UL resource allocations (e.g., each UL resource may be associated with a predefined reference signal sequence). For example, the DCI may grant resources for triggering UL reference signal transmission while providing an explicit reference signal sequence to be used for transmission on the resources. mB may additionally include a 1-bit command indicating a linkage with respect to the reference signal sequence. The link bit may be defined such that if the link bit is 0, the WTRU may clear or reset any previous association between the specified reference signal sequence and the TX beam from the WTRU. The WTRU may consider available or free reference signal sequences to be associated with any TX beam not linked to a valid reference signal sequence. The WTRU may also store a link between the TX beam and a specified reference signal sequence. The WTRU may transmit a UL reference signal on the UL resource by using a TX beam linked to the reference signal sequence. If the link bit is 1, the WTRU may transmit an UL reference signal using the UL resource using a TX beam previously linked to the reference signal sequence.

In other embodiments, the reference signal sequence may be defined in terms of a radio frame number, a subframe number, a symbol, and/or a frequency resource on which the UL reference signal is transmitted. In this method, a WTRU-specific UL reference signal sequence may be allocated and the WTRU may use the same UL reference signal for multiple TX beams.

Alternatively, an mB-based assignment scheme may be deployed for beam IDs rather than reference signal sequence numbers. In an example, the reference signal sequence number may be replaced with a beam ID, and along with the link bits, the mB may control and coordinate the mapping between the beam ID and the WTRU TX beam.

The embodiments described herein with respect to UL data channel beams and pairing can also be used for UL control channel beams. In an example, the UL control channel beam may be characterized as having a wider spatial coverage than the data channel beam. In some embodiments, UL reference signal transmissions for the data channel beam and the control channel beam may coexist or be performed in parallel. For example, a separate set of time and/or frequency UL resources may be reserved for transmitting UL reference signals by using the candidate control channel TX beams. For another example, a separate set of reference signals may be reserved to transmit UL reference signals by using the candidate control channel TX beams. For yet another example, non-overlapping beam ID space may be reserved for control channel beams and data channel beams.

The mB may use the UL reference signal transmitted by the WTRU to evaluate the quality of the UL TX beam. The WTRU may perform UL transmission by using a TX beam associated with a beam ID or reference signal sequence number within the UL grant. The association/mapping between the beam ID or reference signal sequence number and the TX beam ID may be determined based on implicit or explicit WTRU or mB methods as described above. The WTRU may perform UL data transmission by using the UL control beam if the beam ID or reference signal sequence number carries a predefined or reserved value, or if there is no beam information within the scheduling grant.

The mB may determine the timing advance of each WTRU TX beam during the UL reference signal transmission procedure. At least two TX beams from a WTRU may be associated with different timing advance values. The WTRU may apply a timing advance to one or more TX beams based on a timing advance configuration within a MAC message or within a higher layer signaling (e.g., RRC) message. The timing advance value may be indexed with the TX beam ID or UL howline signal serial number. Alternatively, the WTRU may receive RAR messages with individual TX beam responses, or may receive block responses, where each TX beam may be referenced by an RA-RNTI, and the block responses include associated timing advance and/or transmit power settings. The WTRU may apply the same timing advance to two or more TX beams and treat them as belonging to a timing advance group. The WTRU may set an initial transmission of a multi-beam UL reference signal based on the current wide beam PUSCH power. Alternatively, the WTRU may set the maximum power of the UL reference signal beam and may receive closed loop feedback to ramp down the UL transmit power from the maximum power via Transmit Power Control (TPC) bits.

Receivers within the beam-pair link may use beam tracking to update their receive beams, which may increase the SNR during directional data transmission. A transmitter may assist the beam tracking process by transmitting reference signals at predefined locations with reference to actual data transmissions. Beam tracking can be considered as open-loop beam pairing because no feedback from the receiver is required. Beam tracking may enable a receiver to select an optimal RX beam for a given TX beam. Beam tracking may be used to compensate for rapid changes in WTRU heading/blockage, where the amount of spatial shift is small. The reference signal for beam tracking may be referred to as a beam tracking symbol. One or more beam tracking symbols may be pre-added to a data channel (e.g., PDSCH or PUSCH), appended to a data channel (e.g., PDSCH or PUSCH), and/or transmitted to a data channel (e.g., PDSCH or PUSCH) at an offset, where the offset may be positive or negative.

Guard periods may be introduced between beam tracking symbols and/or between beam tracking symbols and data to enable a receiver to evaluate different RX beams. During downlink transmission, the mB may allocate one or more beam tracking symbols to assist WTRU-side RX beam tracking. Similarly, in uplink transmission, the WTRU may transmit one or more beam tracking symbols to enable mB-side RX beam tracking. The resources occupied by the beam tracking symbols may be signaled by using one or more of: semi-static resource allocation via RRX signaling (which may provide, for example, beam tracking symbol resource allocation and/or periodicity); a plurality of PDSCH/PUSCH formats defined to indicate the presence or absence of beam tracking symbols within a given resource allocation; and explicit scheduling for beam tracking symbols (e.g., start and number of beam tracking symbols) similar to scheduling grants of data allocations. Scheduling grants within the DCI may indicate the PDSCH/PUSCH format. The predefined number of beam tracking symbols may be implicitly determined based on the PDSCH/PUSCH format.

In connected mode, the WTRU may monitor one or more control channel beams to receive control information. The control channel beam may be a WTRU-specific control channel beam or a cell-specific common control channel beam. The set of control channel beams that the WTRU may monitor may be referred to as serving control channel beams. The WTRU may be assigned one or more serving control channel beams, or the WTRU may treat all control channel beams from the mB as serving control channels. Alternatively, the WTRU may consider the control channel beam selected during idle mode operation as a WTRU-specific control channel beam for connected mode operation. The WTRU may distinguish the common control channel beam from the WTRU-specific control channel beam by the presence of the predefined beam reference signal. The WTRU may use RX beamforming for additional antenna gain to improve the reliability of the DL control channel. Thus, the concept of beam pairing may be established between the WTRU and the mB. The WTRU-specific search space may be based on, for example, the number of control channel beams transmitted by the mB, the number of control channels selected by the WTRU or assigned to the WTRU, the beam-specific control region size/duration, the overall control region duration, the cell bandwidth, the aggregation level, the WTRU ID, the subframe number, or the subframe. The WTRU-specific search space may be defined as a collection of beam-specific search spaces with all serving control channel beams selected by the WTRU or assigned to the WTRU.

While in connected mode, the WTRU may estimate the suitability of a non-serving control channel beam from the serving cell. The quality of the serving control channel beam may be determined not only by the transmit beam at the mB, but also by the receive beam at the WTRU. The WTRU may provide feedback to the mB based on the evaluation.

Based on the WTRU feedback, the mB may determine a serving control channel beam serving the WTRU based on one or more of: quality of a control channel beam conditioned on receive beamforming at the WTRU, number of WTRUs within a control channel beam and capacity of a control channel, interference of the control channel beam to other co-existing beams from a serving mB, interference of the serving control channel beam to a neighboring cell, and interference of neighboring cell control channels to WTRU receive beams.

The mB may indicate a new serving control channel beam by using RRC signaling or DCI-based signaling. In another embodiment, the WTRU may autonomously select a preferred control channel beam by using one or more of the criteria described above. The WTRU may acquire assistance information from the serving mB to evaluate and select a serving control channel beam. This assistance information may include, for example, an offset or offset value implicitly indicating the control channel capacity, inter-mB interference, and/or BRS threshold to account for the control channel beam used for selection.

The beam switch command from the mB may include one or more of: an identification of a new control channel beam (explicitly or indicated explicitly by a BRS sequence number or from a cell ID), a beamformed data channel associated with the new control channel beam, a configuration for a search space associated with the new control channel beam, resources for UL beamforming (e.g., dedicated RACH preamble and/or time/frequency resources), a backoff TTI associated with a target control channel beam, a beam-specific PCFICH associated with a target control channel beam, resources for transmitting a beam switching ACK (e.g., dedicated PRACH resources with optional repetition, or a beamformed UL PUCCH channel), and/or a UL control channel beam associated with a target control channel beam. The UL control channel beam from the WTRU may be identified by a reference signal sequence ID. In an embodiment, the search space and control channels may be semi-static and may be configured by SIBs. Upon receiving the beam switch command, the WTRU may read the SIBs associated with the control channel beam to determine a new search space. The search space configuration may also include control channel beam to symbol mapping information.

Upon receiving a beam switch command to transition from a source control channel beam to a target control channel beam, the WTRU may: switching its receive beam associated with the target control channel beam to produce a better signal quality metric for the target control channel beam; updating a control channel search space according to the received configuration; adding, modifying or deleting one or more serving control channel beams, and applying a TTI or symbol mapping for the serving control channel beam (this update may take effect at a preconfigured offset of the current TTI); monitoring cell-specific control channel beams in the pre-configured location and WTRU-specific control channels in all other times/locations; ceasing to monitor the source control channel beam and ignoring any pending scheduling grants received on the source control channel beam; updating the UL control channel to the PUCCH configuration; and/or applying the target DL control channel configuration and starting to monitor the target control beam, e.g., by using the new BRS to determine the presence of the target control channel beam.

In case dedicated random access resources are configured, the WTRU may: transmitting a dedicated random access preamble on a pre-configured RACH resource (possibly multiple times depending on a configured repetition factor); performing RACH using one or more UL beams corresponding to the configured target DL control channel beam; and/or receiving a RAR containing a preferred UL beam, which may be identified by a preamble IE or RA-RNTI. The WTRU may use the selected UL beam for ACK/NACK/CSI feedback. The WTRU may additionally receive an updated timing advance corresponding to the new UL transmit beam.

If no random access resources are configured, the WTRU may assume that UL beam information is available at the mB and the WTRU may transmit a beam switch ACK on the PUCCH resources. In an embodiment, the WTRU may transmit the ACK on a preconfigured UL control beam. The timing relationship between the beam switch command and the UL ACK may be predefined or explicitly configured by the beam switch command. In an embodiment, the WTRU may be configured with exactly one UL control beam even though multiple DL control channels are allocated, and the WTRU may transmit the ACK on the configured UL control beam regardless of the DL beam carrying the data.

The WTRU may not reset the MAC/RLC context if the target DL beam configuration is associated with the same serving mB. Additionally, for beam switching between different mbs, different levels of layer 2(L2) reset may be configured at the WTRU. For example, the WTRU may be transparent for beam switching to occur between the same mB, different mbs of the same cell, or different mbs of different cells or clusters. But from the network perspective, different beam switching may result in different levels of L2 reset. The WTRU may be configured to reset only the hybrid automatic repeat request (HARQ) context but retain all ARQ contexts (e.g., sequence numbers), or reset both HARQ and ARQ contexts.

Sometimes, the WTRU may not receive a beam switch command from the mB, or the measurement report to the mB may be lost, e.g., due to a sudden degradation in serving control channel beam quality. This rapid degradation may be due to, for example, dynamic congestion or WTRU orientation changes. In an embodiment, the WTRU may enter an extended monitoring mode and monitor one or more control channel beams in addition to the current serving control channel beam. The extended monitoring mode may provide an additional opportunity for the mB to reach the WTRU and coordinate beam switching procedures to recover the radio link.

When there is a sudden degradation in serving control beam quality, the WTRU may use an active extended monitoring procedure to temporarily increase its beam search space. The terms beam reconstruction and beam recovery are used interchangeably herein. The beam pairing before and after beam reconstruction may be the same or different.

Fig. 11 is a flow diagram 1100 of an exemplary method for extended monitoring implemented in a WTRU. In the example shown in fig. 11, the WTRU may monitor a first control channel Search Space (SS) associated with a first set of standard beams (1102). The first set of standard beams may comprise a first set of beams. The WTRU may monitor a control search space associated with an extended set of beams (1104). Upon initiating and/or entering an extended monitoring mode, e.g., after a trigger based on measurements by the WTRU, the WTRU may perform a control search space associated with the extended set of beams. The trigger may be received from, for example, an mB. The extended set of beams may include a first set of beams and one or more additional sets of beams.

The WTRU may determine a second set of beams from the extended set of beams (1106). The determination may be based on, for example, a received control channel beam switch command or on the SS within which the beam switch command was received. The WTRU may monitor a second control channel, SS, associated with a second set of standard beams (1108). The second set of standard beams may include the determined second set of beams.

In an embodiment, the WTRU may enter extended monitoring based on one or more criteria that may be preconfigured. The criteria may include, for example, one or more serving control beam Beamforming Reference Signal Received Powers (BRSRPs) being below a threshold, one or more non-serving beams BRSRPs being above a threshold, and/or a predefined offset having been reached from a measurement report transmission triggered based on the BRSRPs being above or below the threshold. The BRSRP may be measured, for example, on beamforming reference signals associated with control beams of non-serving control beams, linked PBCH, and/or SYNC beams. In both cases, the threshold may be absolute or relative to one or more other beams within the cell. Additionally or alternatively, the criterion for the WTRU to enter extended monitoring may include the running counter for NACK or CRC failures becoming greater than a predefined value.

In the extended monitoring mode, the WTRU may consider a plurality of different candidate beams for monitoring within an extended set of beams in addition to the first set of beams. The candidate beams may include, for example, one or more of: all control channel beams and/or common control channel beams within the serving cell, one or more control beams or common control channel beams spatially adjacent to the current serving control channel beam (e.g., right and left beams immediately adjacent to the serving control channel beam), a subset of control beams or a subset of common control channel beams explicitly linked to or preconfigured to be associated with the serving control channel beam, one or more control beams or common control channel beams having a quality above a threshold (e.g., the BRSRP threshold described above), one or more control beams or common control channel beams included within the most recent measurement report, and one or more WTRU-specific control channel beams configured as backup beams or candidate beams for extended monitoring.

In the extended monitoring mode, the WTRU may monitor one or more additional beams for one or more TTIs and/or subframes, such as: all subsequent downlink TTIs and/or subframes when the WTRU is in extended monitoring mode; a predefined TTI or subframe specifically configured for extended mode monitoring; all subsequent TTIs or subframes in which the candidate control channel beams are transmitted; and/or TTIs or subframes that carry broadcast signaling (such as PBCH and/or SYNC signals). The WTRU may be configured with a particular control channel beam mapping within one or more of these TTIs and/or subframes. In addition, the WTRU may be configured with specific search spaces and/or DCIs reserved for beam switching control messages.

In an embodiment, the paging message may be used as a beam re-establishment and/or beam switching mechanism. The WTRU may monitor for paging messages in all candidate beams during the extended monitoring mode. The paging type may indicate a reason for beam re-establishment and/or beam switching. The CRNTI may be used as a WTRU identity and additional dedicated resources may be allocated to trigger UL response transmissions from the WTRU.

In an embodiment, the WTRU may explicitly indicate that the extended monitoring mode is entered by transmitting a NACK on a predefined reserved resource (which may be preconfigured on the serving control beam or the standby control beam). Alternatively, the WTRU may transmit the RACH on a pre-configured resource to indicate entry into the extended monitoring mode.

In an embodiment, the WTRU may indicate a preferred beam and an explicit WTRU ID to recover the radio link. One or more RACH preambles or preamble groups and/or time/frequency resources may be pre-configured to implicitly indicate, for example, one or more of: cause the cause of the RACH transmission (e.g., re-establishment, serving control beam below threshold, and/or resource request for measurement report), enter extended monitoring mode, and/or preferred beam set.

The WTRU may exit the extended monitoring mode when one or more conditions are met. This condition may include, for example, receiving a beam switch command within a serving, backup, or other common control beam, and/or not receiving DL DCI and beam switch command within a predefined time from the start of the extended monitoring mode. Upon exiting the extended monitoring mode, the WTRU may perform cell level monitoring or declare a Radio Link Failure (RLF).

Fig. 12 is a flow diagram 1200 of an exemplary method for extended monitoring implemented within a base station, such as a mB. In the example shown in fig. 12, the base station may determine that the WTRU has initiated extended monitoring (1202), and transmit a beam switch command on a condition that the base station determines that the WTRU has initiated extended monitoring (1204). In an embodiment, the WTRU initiating extended monitoring may include, for example, after a measurement-based trigger, switching from monitoring a first control channel SS associated with a first standard set of beams including a first set of beams to monitoring a control channel SS associated with an extended set of beams including the first set of beams and one or more additional sets of beams. The beam switch command may be a command for the WTRU to switch to monitoring a second control channel, SS, associated with a second set of standard beams including a second set of beams.

In an embodiment, the mB may explicitly or implicitly determine that the WTRU has entered an extended monitoring mode. The mB may implicitly determine that the WTRU has entered the extended monitoring mode based on a lack of acknowledgement for the scheduled downlink transmission or a lack of UL data transmission in response to a UL grant. The mB may explicitly determine that the WTRU has entered the extended monitoring mode based on a lack of response to a status query message, a polling request message, a PDCCH order, or other message. The explicit request/response may be faster than the implicit approach and may be more efficient in terms of resource utilization.

To perform beam level monitoring, the WTRU may perform BRS measurements on a PBCH beam linked to a serving control channel beam. The transmission schedule of the PBCH beam may be predefined, such as periodicity and location within the frame structure. The WTRU may additionally or alternatively perform BRS measurements on a common control channel beam linked to the serving control channel beam. The transmission schedule of the common control channel beams may be preconfigured, such as periodicity and location within the frame structure. The WTRU may additionally or alternatively perform opportunistic BRS measurements on the serving control channel beam.

The output of the beam level monitoring may be an average of BRSRP measurements over a predefined time period. The average BRSRP value may indicate a serving control channel beam quality. For beam level monitoring purposes, an in-sync state and an out-of-sync state may be defined based on the measured BRSRP values. The WTRU may determine a beam level failure based on one or more criteria, such as BRSRP measurement being below a predetermined threshold and receiving N consecutive out-of-sync indications.

On a condition that the WTRU determines a beam level failure, it may enter an extended monitoring mode and perform actions designated as part of an extended monitoring procedure. Additionally or alternatively, the WTRU may start monitoring standard and/or fallback DCI in all control channel beams (or a subset thereof) within a subset of TTIs that include the fallback TTI. Additionally or alternatively, the WTRU may determine that the DL beam is lost and may then stop all UL transmissions (which may include ACK/NACK feedback as well as outstanding UL transmissions (which may include measurement reports, higher layer feedback (e.g., RLC ARQ), buffer status reports, and/or any other higher layer data)). Additionally or alternatively, a beam level failure may trigger the WTRU to perform cell level monitoring.

In an embodiment, the WTRU may perform cell level monitoring by performing BRS measurements on all PBCH beams within the current serving cell. Here, the transmission schedule of the PBCH beam may be predefined, such as periodicity and location within the frame structure. Additionally or alternatively, the WTRU may perform cell level monitoring by performing BRS measurements on all common control channel beams within the current serving cell. Here, the transmission schedule of the common control channel beam, such as periodicity and position within the frame structure, may be configured in advance. Additionally or alternatively, the WTRU may perform cell level monitoring by performing BRS measurements on all control channel beams within the current serving cell. Here, for example, periodicity and location within the frame structure, such as within the fallback TTI and/or subframe, may be preconfigured.

In an embodiment, the WTRU may perform cell level monitoring upon the occurrence of a beam level failure, or alternatively, whenever the WTRU enters connected mode. In other embodiments, including in idle mode, the WTRU may be performing cell level monitoring at all times.

If the WTRU finds a suitable beam during cell level monitoring, it may trigger a beam re-establishment or beam handover procedure. The beam re-establishment or beam handover procedure may comprise, for example, performing a RACH procedure to inform the mB that a beam needs to be switched by using, for example, predefined RACH resources for beam re-establishment or beam handover. Additionally or alternatively, the beam re-establishment or beam handover procedure may comprise transmitting a higher layer message indicating beam re-establishment or beam handover by including an old RNTI or measurement report for one or more control channels, e.g. using grants received within the RAR. If a suitable beam is not found during cell level monitoring, such as when a higher layer receives Qout on all control channel beams within the cell, the WTRU may trigger RLF procedures, such as performing cell selection and RRC re-establishment.

Fig. 13A and 13B are diagrams 1300A and 1300B of more specific examples regarding extended monitoring. In the example shown in fig. 13A, mB 1302 scans control channel beams 1304, 1306, 1308, 1310, and 1312 in sequence. In the example shown in fig. 13B, WTRU1320 a monitors the control channel search space associated with control channel beam 1308B (1322). The WTRU1320 may then determine whether an extension mode has been triggered (1324). On a condition that the extension mode has been triggered, the WTRU may continue to monitor the original control channel search space for a beam or set of beams (1322). In the example shown in fig. 13B, WTRU 1320B has been removed so that it is no longer able to receive control channel beam 1308c and so that it is determined that the spreading mode is triggered.

On a condition that the WTRU1320 enters an extended mode, the WTRU1320 determines a control channel beam extension set to monitor (1326) and monitors the extension set for a beam switch command (1328). In the example shown in fig. 13B, WTRU1320 c monitors the extended beams, which include original serving control channel beam 1308d and immediately adjacent beams 1306B and 1308 d. The WTRU1320 may also transmit an indication of a preferred beam on pre-configured resources. On a condition that the beam switch command is not received, the WTRU continues to monitor the extended set (1328). On receiving the beam switch command, the WTRU1320 monitors a new control channel search space including one or more control channel beams (1334). In the example shown in fig. 13B, the new control channel search space includes a new serving control channel beam 1310 c. In an embodiment, the WTRU1320 may optionally wait for a delay time (1332) before monitoring the new control channel search space (1334). In an embodiment, WTRU1320 may optionally send a beam switch ACK (1336) on a condition that WTRU1320 receives the beam switch command.

In at least some embodiments described herein, mB, SCmB, mmW eNB, cell, small cell, Pcell, Scell may be used interchangeably. Further, in at least some embodiments, operations may be used interchangeably with transmission and/or reception. Further, in at least some embodiments, the component carrier and the mmW carrier may be used interchangeably with the serving cell.

In embodiments, the mB may transmit and/or receive one or more mmW channels and/or signals in the licensed band and/or the unlicensed band. In at least some embodiments, the WTRU may be replaced with an eNB and vice versa. Further, in at least some embodiments, the UL may be replaced with DL, and vice versa.

In at least some embodiments, a channel may refer to a frequency band, which may have a center or carrier frequency and a bandwidth. The licensed spectrum and/or the unlicensed spectrum may include one or more channels that may or may not overlap. Channels, frequency channels, wireless channels, and mmW channels may be used interchangeably. An access channel is synonymous with using (e.g., transmitting, receiving, and/or using a channel on) a channel.

In at least some embodiments, a channel may refer to a mmW channel or signal, such as an uplink or downlink physical channel or signal. Downlink channels and signals may include one or more of the following: a mmW synchronization signal, a mmW broadcast channel, a mmW cell reference signal, a mmW beam control channel, a mmW beam data channel, a mmW hybrid ARQ indicator channel, a mmW demodulation reference signal, a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), a demodulation reference signal (DMRS), a cell-specific reference signal (CRS), a CSI-RS, a PBCH, a PDCCH, a PHICH, an EPDCCH, and/or a PDSCH. The uplink channels and signals may include one or more of: mmW PRACH, mmW control channel, mmW data channel, mmW beam reference signal, mmW demodulation reference signal, PRACH, PUCCH, SRS, DMRS, and PUSCH. Channels and mmW channels may be used interchangeably. Channels and signals may be used interchangeably.

In at least some embodiments, data/control can mean data and/or control signals and/or channels. The controlling may include synchronizing. The data/control may be mmW data/control. Data/control and data/control channels and/or signals may be used interchangeably. Channels and signals may be used interchangeably. Control channels, control channel beams, PDCCH, mPDCCH, mmW PDCCH, mmW control channel, directional PDCCH, beamformed control channels, spatial control channels, and control channel slices, high frequency control channels may be used interchangeably. Data channels, data channel beams, PDSCH, mPDSCH, mmW PDSCH, mmW data channels, directional PDSCH, beamformed data channels, spatial data channels, data channel slices, high frequency data channels may be used interchangeably.

In at least some embodiments, the channel resources may be resources such as time, frequency, code, and/or spatial resources (e.g., 3GPP LTE or LTE-a resources), which may carry one or more channels and/or signals, e.g., at least some of the time. In at least some embodiments, channel resources may be used interchangeably with channels and/or signals.

mmW beam reference signals, mmW reference resources for beam measurement, mmW measurement reference signals, mmW channel state measurement reference signals, mmW demodulation reference signals, mmW sounding reference signals, CSI-RS, CRS, DM-RS, DRS, measurement reference signals, reference resources for measurement, CSI-IM, and measurement RS may be used interchangeably. mmW cells, mmW small cells, scells, secondary cells, licensed secondary cells, unlicensed cells, and LAA cells may be used interchangeably. mmW cells, mmW small cells, PCell, primary cells, LTE cells, and licensed cells may be used interchangeably. Interference and interference noise may be used interchangeably.

The WTRU may determine the UL and/or DL direction of one or more subframes according to one or more received and/or configured TDD UL/DL configurations. UL/DL and UL-DL may be used interchangeably.

The embodiments described herein may be applicable to any system regardless of frequency band, usage (e.g., licensed, unlicensed, shared), antenna configuration (e.g., phased array antenna, patch antenna, or horn antenna), RF configuration (e.g., single RF chain or multiple RF chains), beamforming methods used (e.g., digital, analog, hybrid, codebook-based, or other methods), deployment (e.g., macro-cell, small cell, heterogeneous network, dual connectivity, remote radio head, or carrier aggregation). In some embodiments, mmW may be replaced with cmW or LTE/LTE-a/LTE evolved, LTE advanced, or LTE advanced Pro.

In at least some embodiments, a scheduling interval may refer to a subframe, a slot, a frame, a schedulable slice, a control channel periodicity, or any other predefined unit of time. Gaps, guard periods, silence periods, switching periods, transmission absence, or DTX periods may be used interchangeably.

Antenna patterns, phase weights, steering vectors, codebooks, precoding, radiation patterns, beam patterns, beams, beamwidths, beamformed transmissions, antenna ports, virtual antenna ports, or transmissions associated with particular reference signals, directional transmissions, or spatial channels may be used interchangeably.

In the embodiments described herein, the radiation pattern may refer to an angular distribution of the radiated electromagnetic field or a power level in a far-field region. Further, in an embodiment, a beam may refer to one of the lobes, such as the main lobe, side lobe and/or grating lobe of the transmit radiation pattern and receive gain pattern of an antenna array ([ ]). A beam may also represent a spatial direction that may be represented by a beamforming weight vector. A beam may be identified or associated with a reference signal, antenna port, beam Identification (ID), and/or scrambling sequence number and may be transmitted and/or received at a particular time resource, frequency resource, code resource, and/or spatial resource. The beams may be formed digitally, analog, or both (e.g., hybrid beamforming). Analog beamforming may be based on a fixed codebook or continuous phase shift. The beams may also include omni-directional transmissions or quasi-omni transmissions. The two beams may be distinguished by the direction of highest radiated power and/or by the beam width.

In an embodiment, a data channel beam, a PDSCH, an mPDSCH, an mmW PDSCH, an mmW data channel, a directional PDSCH, a beamformed data channel, a spatial data channel, a data channel slice, or a high frequency data channel may be transmitted using the data channel beam. A data channel beam may be identified or associated with a reference signal, an antenna port, a beam Identification (ID), a scrambling sequence number, or a data channel number, and may be transmitted and/or received at a particular time resource, frequency resource, code resource, and/or spatial resource.

In an embodiment, a control channel beam may be used to transmit a control channel, PDCCH, mPDCCH, mmW PDCCH, mmW control channel, directional PDCCH, beamformed control channel, spatial control channel, control channel slice, or high frequency control channel. The control channel may carry DCI for one or more users. The control channel may also carry PHICH and PCFICH in the downlink and PUCCH in the uplink. A control channel beam may be identified or associated with a reference signal, antenna port, beam Identification (ID), scrambling sequence number, or control channel number and may be transmitted and/or received at a particular time resource, frequency resource, code resource, and/or spatial resource. The control channel beams may be cell-specific or WTRU-specific.

In an embodiment, a common control channel beam may refer to a control channel beam that may be used to carry control information associated with broadcast or multicast information (such as SI, paging, and/or beam switch commands).

In an embodiment, the Half Power Beamwidth (HPBW) may refer to the angle between the two directions of 1/2 where the radiation intensity is at a maximum within the radiation pattern cut (cut) containing the direction of the largest lobe. The exact beamwidth of the beamformed control/data channel may not be specified but may depend on the mB or WTRU implementation. The mB may support WTRUs with varying capabilities and vice versa.

In an embodiment, the control channel beam duration may refer to the number of OFDM symbols occupied by one control channel beam within the scheduling time interval. The control region may be the number of OFDM symbols occupied by all control channel beams transmitted in a scheduling time interval within the scheduling time interval.

In an embodiment, fixed codebook-based analog beamforming may refer to a beam grid, which may comprise or consist of a fixed set of beams. Each beam is selectable by applying a code book selected from a predefined code book v e v₁,v₂,v₃…v_NIs formed, where N represents the number of fixed beams. The number of beams may depend on the HPBW for the desired coverage and beamforming.

In an embodiment, continuous phase-shift analog beamforming may refer to a desired weight for each phase shifter calculated based on estimated channel information (e.g., angle information translated for application to the phase shifter using a high-resolution digital-to-analog converter (DAC)). Continuous and adaptively adjusted beamforming may be provided to track channel conditions.

In an embodiment, an antenna port may be defined such that a channel on which a symbol on the antenna port is communicated may be inferred by a channel on which another symbol on the same antenna port is communicated. There may be one resource grid per antenna port.

In an embodiment, a link may refer to a predefined offset between two channels and/or beams. The link may be used to determine the transmission schedule, time, frequency location of one channel and/or beam when the time and/or frequency location of another channel/beam is known.

In an embodiment, BRSRP may be defined as the average power received by a WTRU from beam-specific reference signal resource elements associated with a control channel beam. In an embodiment, cells, 5G cells, mmW cells, transmission points, and clusters may be used interchangeably.

Although the features and elements of the present invention are described above in particular combinations, it will be understood by those of ordinary skill in the art that each feature or element can be used alone without the other features and elements or in various combinations with any other features and elements of the present invention. Furthermore, the methods described herein may be implemented in a computer program, software, or firmware executed by a computer or processor, where the computer program, software, or firmware is embodied in a computer-readable storage medium. Examples of computer readable media include electronic signals (transmitted over a wired or wireless connection) and computer readable storage media. Examples of computer readable storage media include, but are not limited to, Read Only Memory (ROM), Random Access Memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media (e.g., internal hard disks or removable disks), magneto-optical media, and optical media such as CD-ROM disks and Digital Versatile Disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims (4)

1. A base station, comprising:

a processor; and

a transceiver for receiving and transmitting a signal from a base station,

the processor and the transceiver are configured to determine that a wireless transmit/receive unit (WTRU) has initiated extended monitoring, which includes switching from monitoring a first control channel Search Space (SS) associated with a first standard beam set including a first beam set to monitoring a control channel (SS) associated with an extended beam set including the first beam set and one or more additional beam sets after a measurement-based trigger, and

the processor and the transceiver are further configured to transmit a beam switch command for the WTRU to switch to monitoring a second control channel, SS, associated with a second set of standard beams including a second set of beams on a condition that the processor and the transceiver determine that the WTRU has initiated extended monitoring.

2. The base station of claim 1, wherein the base station is further configured to,

the processor and the transceiver are further configured to determine that the WTRU has initiated extended monitoring based on one or more of: the transceiver does not receive an Acknowledgement (ACK) for a scheduled Downlink (DL) transmission, the transceiver does not receive an Uplink (UL) data transmission in response to a UL grant, and the transceiver does not receive a response to at least one of: a status query message, a polling request message, or a Physical Downlink Control Channel (PDCCH) command or other message.

3. The base station of claim 1, wherein the beam switch command comprises at least one of: an identification of the second set of beams, a beamformed data channel associated with the second set of beams, a configuration for the second control channel SS, resources for UL beamforming, a backoff Transmission Time Interval (TTI) associated with the second set of beams, a beam-specific physical control format indicator channel (PDFICH) associated with the second set of beams, resources for transmitting a beam switch ACK, and a UL control channel beam associated with the second set of beams.

4. The base station of claim 1, wherein the beam switch command is indicated using a paging message.

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